The illicit synthesis of phenyl-2-propanone (P2P) in clandestine drug laboratories from phenylacetic acid and acetic anhydride in the presence of sodium acetate or pyridine, or from the dry distillation of phenylacetic acid and lead (II) acetate is examined. These two routes are investigated using capillary gas chromatography (GC) combined with vapor-phase Fourier transform infrared (FTIR) spectroscopy and electron impact mass spectrometry (EIMS) detection (GC-FTIR-EIMS), and using nuclear magnetic resonance (NMR) spectroscopy to identify 21 reaction by-products. The mechanisms of the two reactions producing P2P are presented, along with the mechanisms giving rise to these by-products. This investigation has identified 4 reaction-specific compounds which can be used to differentiate the two synthetic methods.